Hubble Found a Giant Ten-Sided Wave Around Saturn’s South Pole
Hubble observations have revealed a vast, evolving decagon embedded in a jet stream around Saturn’s south pole. The wave spans several atmospheric layers and may have formed recently, but scientists still do not know what triggered it or whether it will endure like the planet’s northern hexagon.
Quick summary
Hubble observations have revealed a vast, evolving decagon embedded in a jet stream around Saturn’s south pole. The wave spans several atmospheric layers and may have formed recently, but scientists still do not know what triggered it or whether it will endure like the planet’s northern hexagon.
A new shape in Saturn’s weather
Astronomers have identified a ten-sided atmospheric wave encircling Saturn’s south pole, the first large regular polygon seen in the planet’s southern hemisphere. The result was published on September 2 in Science Advances after researchers combined NASA and ESA Hubble images with observations contributed by professional and amateur astronomers on Earth.
The structure sits near 63 degrees south inside a powerful eastward jet. One side is longer than 16,700 kilometres, making the full pattern wider than Earth many times over. Unlike Saturn’s famous northern hexagon, which is nearly stationary and has remained visible for more than four decades, the southern decagon drifts eastward at about 10 kilometres per hour.
The remarkable part is not merely the number of sides. Saturn appears to be building a planetary-scale weather pattern while astronomers are watching.
How the decagon emerged
Hints of the wave appear in Hubble data from 2023. Ground-based observers noticed a subtle disturbance in 2024, and images from 2025 showed all ten vertices more clearly. Earlier views from the Cassini spacecraft, which studied Saturn until 2017, did not reveal a comparable long-lived structure. That suggests the feature may have formed during the years when the south pole was tilted away from Earth.
Images taken through different filters place the visible part of the wave in the upper troposphere and show that it extends through several atmospheric heights. Winds associated with it reach roughly 400 kilometres per hour. Researchers also noticed a nearby anticyclonic vortex that darkened before the decagon became prominent, raising the possibility that the vortex helped start the disturbance.
Simple fluid models can produce polygonal waves when a rotating jet becomes unstable, but they do not yet explain why this pattern has ten sides, why it appeared now, or why Saturn’s opposite pole supports a six-sided structure. Comparing both poles could improve models of weather on giant planets.
Reality check
The decagon is an observed cloud and jet-stream pattern, not a solid structure and not evidence of a new object near Saturn. Its exact three-dimensional shape, chemical colouring, formation mechanism and lifetime remain uncertain. Continued Hubble, Webb and ground-based monitoring will show whether it stabilizes or fades.
What comes next
Saturn’s changing seasons will make the southern hemisphere easier to observe during the next several years. The team plans to track the wave’s speed, contrast and depth, then test more detailed atmospheric simulations. Those measurements may reveal whether scientists caught a brief disturbance or the birth of a second enduring planetary polygon.
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